The escalating demand for concrete in infrastructure development and the concurrent depletion of natural fine aggregates has necessitated urgent research into sustainable supplementary materials.  A systematic and experimental investigation into the use of Ground Granulated Blast Furnace Slag (GGBFS) and Wood Ash (WA) to partially replace fine aggregate in M25-grade concrete is presented in this thesis. Wood ash, an industrial and agricultural by-product generated from biomass combustion in thermal power plants, brick kilns, and sugar mills, and GGBFS, a latent hydraulic by-product of pig iron manufacturing, are abundantly available in India and pose significant environmental disposal challenges when unutilized.  The study employs a systematic experimental design wherein WA and GGBFS are used individually and in combined proportions (0%, 5%, 10%, 15%, and 20% by weight of fine aggregate) to assess fresh and hardened concrete properties.  Workability (slump cone test), compressive strength (7-day and 28-day), split tensile strength, flexural strength, and water absorption were all tested in accordance with the applicable guidelines set forth by the Bureau of Indian Standards (BIS). The cost analysis of ash processing for carbon removal and the confirmation that the used wood ash does not contain unburned carbon—a factor that has a significant impact on the microstructure and hydration of concrete—are crucial components of this investigation. Experimental results indicate that optimum replacement levels of WA and GGBFS yield concrete with mechanical properties meeting or exceeding the M25 design strength of 25 N/mm².  The findings support the feasibility of utilizing these industrial by-products in concrete manufacturing, thereby contributing to sustainable construction practices, waste reduction, and partial conservation of natural river sand resources.